1. Field of the Invention
The present invention relates to a glass lining application method for glass-lined instruments having a stainless steel plate or casting as a base material capable of withstanding severe service conditions in the chemical industry, the pharmaceutical industry, the food industry, etc.
2. Description of the Related Art
In the firing of glass linings, a base metal must be an oxidizable metal so that a ground coat can adhere to the base metal firmly. Since stainless alloys are nonoxidizable, in the case of glass lining on stainless base materials, attempts have conventionally been made to roughen a surface of the stainless base material and increase bonding with the ground coat chemically by acid treatment of the surface during precleaning or by means of a physical sandblasting treatment.
Furthermore, in glass linings on stainless base materials, differences in the coefficients of linear thermal expansion of the stainless base materials (coefficients of linear thermal expansion equal to or greater than 165xc3x9710xe2x88x927xc2x0 C.xe2x88x921 at 100 to 400xc2x0 C.) and glasses (coefficients of linear thermal expansion of 95 to 100xc3x9710xe2x88x927xc2x0 C.xe2x88x921 at 100 to 400xc2x0 C.) are large, and residual compression stresses after the firing process due to differences in cooling contraction are great, giving rise to the occurrence of shearing stresses from the stainless base material to the glass lining layer, whereby delamination of the glass lining layer often occurs.
In order to solve problems such as that described above when applying a glass lining to a stainless base material, Japanese Patent No. 2642536, for example, discloses a glass lining application method in which a thermal spray treatment is applied to a surface of a stainless base material using a thermal spray material selected from a group composed of a stainless material identical to the base material, Ni metal, Cr metal, Fe metal, Co metal, Nixe2x80x94Cr alloys, and Fexe2x80x94Cr alloys, and then glass lining is performed by means of a heat treatment, the glass lining application method being characterized in that a total glass lining thickness is within a range from 600 xcexcm to 2500 xcexcm, and a ratio between a thermal spray treatment layer thickness and the glass lining layer thickness is within a range from 1:10 to 1:200. Bond strength between the stainless base material and the ground coat layer can be ensured to a certain extent by the glass lining application method according to this patent, enabling a glass lining structure having superior glass lining delamination resistance to be provided.
However, since plasma spray treatments at the time when the above patent was invented involved an operator manually securing the base material and spraying a thermal spray gun, the only possible parameter for increasing bond strength and suppressing delamination of the glass lining in the thermal spray treatment using a thermal spray material on stainless base materials in large shapes was to perform an operation such as regulating the ratio between the thermal spray treatment layer thickness and the glass lining layer thickness as described above during the thermal spray treatment using a thermal spray material on the stainless base material and during subsequent formation of the glass lining layer by means of a ground coat and cover coat.
However, in conventional manual plasma spray treatments, the temperature of the thermal spray formed by an arc discharge is approximately 10,000xc2x0 C. and the globule temperature of the thermal spray material is only around 3,000 to 4,000xc2x0 C., making the grains in the globules of the thermal spray material coarse, thereby making it difficult to form a uniform thermal spray treatment layer on stainless base materials in large shapes. In other words, if the thermal spray material adheres to the stainless base material surface before globule formation and size reduction can progress sufficiently, the resulting thermal spray treatment layer may be locally thickened, the surface of the thermal spray treatment layer may be coarse, or an open pore diameter of the thermal spray treatment layer surface may be abnormally large, exceeding 100 xcexcm, and the present inventors found by means of subsequent experiments with actual specimens having large shapes that there was a possibility that problems such as bubbles being generated in the glass lining layer or bond strength between the ground coat layer and the stainless base material deteriorating would arise if a glass lining is applied to a thermal spray material layer of this kind. In other words, it was found that when applying glass linings to stainless base materials in large shapes, there are cases when it is insufficient merely to control the ratio between the thermal spray treatment layer thickness and the glass lining layer thickness.
Consequently, an object of the present invention is to provide a new glass lining application method enabling stable, uniform glass lining layers to be applied to large glass-lined instruments composed of a stainless base material.
Remarkable progress in thermal spray treatment techniques has been accomplished in recent years, and automated (robotized) plasma thermal spraying techniques constitute the mainstream. According to this thermal spraying technique, thermal spray temperatures in excess of 10,000xc2x0 C. are achieved by means of an arc discharge, and globule temperatures have also risen to 5,000 to 6,000xc2x0 C. therewith, enabling thermal spray material to be formed into globules, reduced in size, accelerated, and ejected in a high-temperature range. The present inventors have applied this thermal spraying technique to the thermal spraying of stainless base materials in large shapes, and have found therewith that the technique is effective for applying stable, uniform glass lining layers to glass-lined instruments composed of stainless base materials in large shapes if surface roughness of a thermal spray treatment layer, open pore diameter, and bond strength between a ground coat layer and the thermal spray-treated stainless base material are kept within certain ranges by controlling the surface characteristics of a thermal spray treatment layer formed thereon.
According to one aspect of the present invention, there is provided a glass lining application method including forming a thermal spray treatment layer by applying a thermal spray treatment to a surface of a stainless base material using a thermal spray material selected from a group composed of a stainless material identical to the base material, Ni metal, Cr metal, Fe metal, Co metal, Nixe2x80x94Cr alloys, and Fexe2x80x94Cr alloys, then forming a glass lining layer on the thermal spray treatment layer by means of a glass lining heat treatment using a ground coat and a cover coat,
wherein:
a surface roughness Rz of the thermal spray treatment layer is within a range from 5 to 100 xcexcm; and
an open pore diameter is within a range from 3 to 60 xcexcm.
A bond strength between the thermal spray-treated stainless base material and the ground coat glass lining layer may be equal to or greater than 250 N/cm2 (2.5 MPa).
A thickness of the glass lining layer may be within a range from 600 xcexcm to 2500 xcexcm.
A thickness of the thermal spray treatment layer and a thickness of the glass lining layer may be within a range from 1:10 to 1:200.